Friction Stir Welding Thermal Control Using Copper Sheet
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Solution Overview
Problem
Friction welding of thin metal parts with low thermal conductivity poses challenges in temperature control, leading to rapid exothermicity and potential deformation, making it difficult to achieve a stable viscous state for recrystallization and resulting in reduced productivity and mechanical quality.
Innovation Solution
A method involving a main sheet with high thermal conductivity placed against the parts to capture and dissipate heat, combined with optional secondary sheets, to regulate temperature and prevent localized overheating, using a mandrel with a shoulder for friction heating and recrystallization, while avoiding complex tooling and invasive procedures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If friction welding is performed on thin metal parts with low thermal conductivity, then welding temperature can be achieved, but localized rapid exothermicity occurs causing deformation and preventing stable viscous state
Solution Approach 1:
A copper sheet with high thermal conductivity is introduced as an intermediary element between the anvil and the thin metal parts. This copper sheet acts as a heat sink that rapidly conducts away excess heat from the weld zone, preventing localized rapid exothermicity and material deformation while maintaining the necessary welding temperature through friction heating.
Solution Approach 2:
The thermal conductivity parameter of the system is changed by introducing a copper sheet with high thermal conductivity (k=400 W/m·K) compared to the thin metal parts with low thermal conductivity. This parameter change enables rapid heat dissipation from the weld zone, controlling the temperature profile to achieve stable viscous state without excessive temperature rise.
2Power
If forceful working of mandrel with shoulder is used, then heating efficiency is improved, but localized rapid temperature rise causes material to exceed melting temperature
Solution Approach 1:
The copper sheet serves as a thermal mediator that decouples the heating process from the heat accumulation problem. It allows forceful mandrel working to generate necessary heating power while simultaneously conducting excess heat away, preventing the weld zone temperature from exceeding the melting temperature of the base material.
Solution Approach 2:
The potentially harmful localized rapid exothermicity is converted into a beneficial effect by using the copper sheet to capture and distribute this heat. The heat that would otherwise cause excessive temperature rise and material degradation is instead used to maintain stable viscous state for proper material mixing and recrystallization.
3Productivity
If traditional transient step is used to evaluate welding characteristics, then initial welding parameters can be determined, but reliable definition of effusion conditions cannot be achieved for thin parts with low thermal conductivity
Solution Approach 1:
The copper sheet is pre-positioned on the anvil before the welding operation begins. This preliminary action ensures that the thermal management system is in place before friction heating starts, allowing immediate heat dissipation control and enabling reliable achievement of effusion conditions from the outset, rather than requiring extensive transient evaluation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for efficient temperature control, increasing production speeds, ensuring high-quality welds with stable recrystallization characteristics and mechanical properties, while protecting the weld bead from thermal stresses and deformation.
Implementation Method 1
maintaining a main sheet (19) made from a material with high thermal conductivity flat against the lower faces (12, 13) of the parts (1, 2)... the main sheet (19)... capable of picking up by conduction the heat induced by the friction
Implementation Method 2
friction exerted locally on them by the welding pin in the weld zone... the friction of the welding pin and the shoulder cause the material from which the parts come from to heat up
Implementation Method 3
The joint between the parts is then obtained by continuous dynamic recrystallization of the material in the weld zone
Data Source
Figure 1~3
Figure 4~7
AI summary
The invention relates to a friction welding method between two thin, flat parts (1, 2) to be joined. A main sheet (19) made of a material with high thermal conductivity is held against the parts (1, 2) to be joined. This main sheet (19) absorbs heat induced by the friction of a welding pin (5) against the parts (1, 2) to form the weld bead, and dissipates this heat by radiation. The main sheet (19) provides thermal regulation for the welding operation, preventing localized heat buildup in the weld zone. The main sheet (19) is copper-based and thinner than the parts (1, 2).